When using "-seccomp on", the seccomp policy is only applied to the
main thread, the vcpu worker thread and other worker threads created
after seccomp policy is applied; the seccomp policy is not applied to
e.g. the RCU thread because it is created before the seccomp policy is
applied and SECCOMP_FILTER_FLAG_TSYNC isn't used.
This can be verified with
for task in /proc/`pidof qemu`/task/*; do cat $task/status | grep Secc ; done
Seccomp: 2
Seccomp: 0
Seccomp: 0
Seccomp: 2
Seccomp: 2
Seccomp: 2
Starting with libseccomp 2.2.0 and kernel >= 3.17, we can use
seccomp_attr_set(ctx, > SCMP_FLTATR_CTL_TSYNC, 1) to update the policy
on all threads.
libseccomp requirement was bumped to 2.2.0 in previous patch.
libseccomp should fail to set the filter if it can't honour
SCMP_FLTATR_CTL_TSYNC (untested), and thus -sandbox will now fail on
kernel < 3.17.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
qemu-seccomp.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index f0c833f3ca..4729eb107f 100644
--- a/qemu-seccomp.c
+++ b/qemu-seccomp.c
@@ -149,6 +149,11 @@ static int seccomp_start(uint32_t seccomp_opts)
goto seccomp_return;
}
+ rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
+ if (rc != 0) {
+ goto seccomp_return;
+ }
+
for (i = 0; i < ARRAY_SIZE(blacklist); i++) {
if (!(seccomp_opts & blacklist[i].set)) {
continue;
--
2.18.0.547.g1d89318c48